In the human nervous system, signals are transmitted along neurons as "action potentials" that travel at speeds of up to 100 m/s. (an action potential is a traveling influx of sodium ions through the membrane of a neuron.) the signal is passed from one neuron to another by the release of neurotransmitters in the synapse. suppose someone steps on your toe. the pain signal travels along a 1.2 m long sensory neuron to the spinal column, across a synapse to a second 1.2 m long neuron, and across a second synapse to the brain. suppose that the synapses are each 109 nm wide; that it takes 0.10 ms for the signal to cross each synapse; and that the action potentials travel at 92 m/s.